U.S. patent number 4,921,652 [Application Number 07/229,797] was granted by the patent office on 1990-05-01 for process for producing a porous film.
This patent grant is currently assigned to Mitsui Toatsu Chemicals, Inc.. Invention is credited to Michiyasu Ito, Syoichi Ito, Shuji Matsumura, Hisatosi Suzuki, Syoichi Tsuji.
United States Patent |
4,921,652 |
Tsuji , et al. |
May 1, 1990 |
Process for producing a porous film
Abstract
A process for producing a porous film having practically
sufficient mechanical strengths, good flexibility, uniform fine
pores and high moisture vapor permeability, and further an
extremely thin porous film, which process comprises blending 30 to
80 parts by weight of an inorganic fine powder having a specific
surface area of 15 m.sup.2 /g or less and an average particle size
of 0.4 to 4 .mu.m with 20 to 70 parts by weight of a polyolefin
resin, followed by melt-molding the resulting blend into a film and
then stretching the film to 2 to 7 times the original length at
least in the uniaxial direction.
Inventors: |
Tsuji; Syoichi (Aichi,
JP), Ito; Syoichi (Aichi, JP), Matsumura;
Shuji (Aichi, JP), Suzuki; Hisatosi (Aichi,
JP), Ito; Michiyasu (Mie, JP) |
Assignee: |
Mitsui Toatsu Chemicals, Inc.
(Tokyo, JP)
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Family
ID: |
17723294 |
Appl.
No.: |
07/229,797 |
Filed: |
August 8, 1988 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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945706 |
Dec 23, 1986 |
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Foreign Application Priority Data
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Dec 23, 1985 [JP] |
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60-287909 |
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Current U.S.
Class: |
264/41;
264/DIG.47 |
Current CPC
Class: |
C08J
5/18 (20130101); C08K 3/013 (20180101); C08K
3/013 (20180101); C08L 23/02 (20130101); C08J
2323/04 (20130101); C08J 2323/02 (20130101); Y10S
264/47 (20130101) |
Current International
Class: |
C08J
5/18 (20060101); C08K 3/00 (20060101); B29C
067/20 (); B29C 055/04 () |
Field of
Search: |
;264/DIG.47,41,145,154 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0066672 |
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Mar 1982 |
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EP |
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2505251 |
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May 1982 |
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FR |
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2027637 |
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Aug 1978 |
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GB |
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2151538 |
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Dec 1984 |
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GB |
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Primary Examiner: Lowe; James
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak &
Seas
Parent Case Text
This is a continuation of application Ser. No. 06/945,706 filed
12/23/86, now abandoned.
Claims
What we claimed is:
1. A process for producing a porous film which consists essentially
of blending 30 to 80 parts by weight of an inorganic fine powder
having a specific surface area of 15 m.sup.2 /g or less, an average
particle size of 0.4 to 4 .mu.m and a spherical particle shape,
selected from the group consisting of precipitated calcium
carbonate, barium sulfate, precipitated barium sulfate, magnesium
carbonate, magnesium oxide, silica, aluminum hydroxide and alumina
with 20 to 70 parts by weight of a polyolefin resin, these parts by
weight being based on 100 parts by weight of the blend, followed by
melt-molding the resulting blend into a film and then stretching
the film to 2 to 7 times the original length at least in the
uniaxial direction.
2. A process according to claim 1 wherein said polyolefin resin is
a linear low density polyethylene resin or a blend containing the
same.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for producing a porous film
having flexibility and a structure of uniform fine pores and hence
superior water vapor permeability and water resistance and useful
for waterproof clothings, waterproof covers, packaging materials,
etc.
2. Description of the Related Art
There has so far been known a process for producing a porous film
by blending non-compatible substances such as inorganic fine
powders with a polyolefin resin in a specified proportion, followed
by melt-molding the resulting blend into a film or sheet and then
uniaxially or biaxially stretching the film or sheet.
However, such a process has had a drawback that since the resin is
stretched and oriented by stretch processing, the film or sheet
increases in the hardness so that its flexibility is damaged.
In order to overcome such a problem, the following processes for
producing a porous film have been proposed:
(1) a process of blending a thermoplastic elastomer with a
polyolefin resin and a filler (Japanese patent application
laid-open No. Sho 59-30833/1984);
(2) a process of blending a liquid or waxy hydrocarbon polymer with
a polyolefin resin and a filler (U.S. Pat. No. 4,472,328); and
(3) a process of blending barium sulfate as an inorganic fine
powder with a polyolefin resin (G.B. No. 2,151,538).
However, porous films obtained according to these production
processes have the following practical drawbacks:
According to the process (1), the resulting porosity is
insufficient and the water vapor permeability is inferior.
According to the process (2), the resulting porous film has a
problem that in the high temperature atmosphere or after a long
time lapse, hydrocarbon polymers bleed out on the surface of the
resulting film so that the surface is sticky. According to the
process (3), the resulting porous film has a good flexibility and
sufficient water vapor permeability, but the stretching stability
i.e. the high stretchability is inferior. Further, as a problem in
common to these processes, it is impossible to produce an extremely
thin film of about 20.mu.. Furthermore, another process of blending
a third component brings about a large increase in cost.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a process for
producing a porous film which comprises a polyolefin resin having a
superior solvent resistance, and has practically sufficient
mechanical strengths and a good flexibility and also has uniform
fine pores and high moisture vapor permeability, and further an
extremely thin porous film.
The present invention resides in a process for producing a porous
film which comprises blending 30 to 80 parts by weight of an
inorganic fine powder having a specific surface area of 15 m.sup.2
/g or less and an average particle size of 0.4 to 4 .mu.m with 20
to 70 parts by weight of a polyolefin resin, these parts by weight
being based on 100 parts by weight of the blend, followed by
melt-molding the resulting blend into a film and then stretching
the film to 2 to 7 times the original length at least in the
uniaxial direction.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Examples of the polyolefin resin used in the present invention are
polypropylene, low density polyethylene, linear low density
polyethylene, high density polyethylene and mixtures thereof. Among
these, linear low density polyethylene and blends containing linear
low density polyethylene are particularly preferred. Examples of
the comonomer component for linear low density polyethylene are
generally butene, 4-methylpentene, hexene, octene, decene, etc. and
among these, 4-methylpentene and octene are preferred in the aspect
of moldability and physical properties of products.
The inorganic fine powder used in the present invention is fine
particles having a specific surface area of 15 m.sup.2 /g or less
and an average particle size of 0.4 to 4 .mu.m. Examples of the
inorganic fine powder used in the present invention are calcium
carbonate, magnesium carbonate, magnesium oxide, barium sulfate,
silica, aluminum hydroxide, alumina, etc. Among these, precipitated
calcium carbonate and precipitated barium sulfate are preferred
since such materials have a uniform particle diameter and specific
surface area and when they are blended with the resin component and
the resulting blend is molded, they have superior dispersibility
and the blend has superior processability. Further, the inorganic
fine powder is preferred to have a spherical shape. Precipitated
barium sulfate is usually obtained for example by the reaction of
barium sulfide with an aqueous solution of sodium sulfate or the
reaction of barium sulfide with sulfuric acid. The shape includes
amorphous shape, spindle shape, plate shape, diamond shape,
spherical shape, etc. When the concentrations of barium sulfide and
SO.sub.4.sup.2-, the mechanical conditions of the reaction and the
reaction temperature are set under specified conditions,
precipitated barium sulfate having a desired average particle size
is obtained.
Further, the precipitated calcium carbonate is usually formed by
introducing carbon dioxide into an aqueous suspension of calcium
hydroxide. It has a cubic shape having an average particle size of
1.mu. or less or a spindle shape or an acicular shape having an
average particle size of 1.mu. or more. When the reaction
temperature of the aqueous suspension of calcium hydroxide,
addition of a particular salt and the termination time of the
reaction are set under specified conditions, a spherical
precipitated calcium carbonate having a desired average particle
size is obtained.
The specific surface area of the inorganic fine powder is 15
m.sup.2 /g or less and a range of 0.5 to 5 m.sup.2 /g is preferred.
If the specific surface area exceeds 15 m.sup.2 /g, the shape of
the inorganic fine powder becomes amorphous shape, plate shape or
acicular shape so that the particle size distribution becomes broad
and the stretchability of film becomes lowered; hence no good
porosity is obtained. Further, the porosity of the surface of the
fine powder increases and due to the volatile components such as
moisture attached to the pores, foaming is observed at the time of
melt-molding the pore size of the resulting film is increased and
its water-resistant is remarkably reduced.
The average particle size of the inorganic fine powder is
preferably in the range of 0.4 to 4 .mu.m, more preferably in the
range of 0.6 to 2 .mu.m. If the average particle size exceeds 4
.mu.m, the stretchability of the film is inferior and stretching
breakage occurs prior to uniform stretching. Thus, the production
stability is inferior to make uniform pore-formation
impossible.
On the other hand, if the average particle size is less than 0.4
.mu.m, the mineral fine powder cannot be highly filled to be unable
to make the resulting film porous.
In the resin composition of the present invention, the quantity of
the inorganic fine powder is in the range of 30 to 80 parts by
weight, preferably 30 to 70 parts by weight based on 100 parts by
weight of the blend. With the quantity of less than 30 parts by
weight, no good porosity can be obtained in respect of the
stretched film. If the quantity exceeds 80 parts by weight,
kneadability, dispersibility and stretchability are inferior; thus
naturally the water vapor permeability is also inferior and the
flexibility lowers.
Next, the process for producing the porous film of the present
invention will be described. First, an inorganic fine powder is
mixed with a polyolefin resin in specified proportions. The mixing
process has no particular limitation. In general, the materials are
mixed by means of a blender or the like, followed by blending the
mixture by means of a Banbury mixer or another melt-kneader in
advance, thereafter pelletizing the blend or not pelletizing it and
then sheeting by means of a conventional sheet-molding machine. It
is possible to optionally add various additives such as lubricant
e.g. calcium stearate, pigment, stabilizers such as those against
heat, light and others, plasticizers, antistatic agent, etc.
The film is generally made by calendering, casting or extrusion,
but among these, extrusion using a circular die or a T-die is
preferred. The extruded sheet is then at least in the uniaxial
direction stretched in a stretching ratio of 2 to 7 times at the
softening temperature or lower of the polyolefin resin according to
a known process. Among the above range of the stretching ratio, 4
to 6 times are preferred. If the stretching ratio is less than 2
times, it is difficult to obtain a good water vapour permeability,
while if it exceeds 7 times, stretching breakage occurs to make
stabilized production impossible.
The present invention will be described in more detail by way of
Examples. Physical properties of the film were evaluated according
to the following methods:
Specific surface area (m.sup.2 /g): measured according to BET
adsorption method.
Average particle size (.mu.m): measured by means of an instrument
for measuring the powder surface area (manufactured by Shimazu
Seisakusyo), by filling its sample (3 g) in a sample cylinder of 2
cm.sup.2 .times.1 cm and measuring the time of air permeation (5
cc) under 50 mm water pressure.
Tensile strength at break (kg): according to JIS P-8113 using
samples of 25 mm wide.times.100 mm long; grip separation rate 200
mm/min., the tensile strength at break was measured MD (machine
direction) and in TD (traverse direction to MD), respectively.
Water vapor permeability: measured according to ASTM-E-96-66.
Softness: Evaluation was made by hand touch as follows:
A: very soft
B: somewhat soft
C: considerably hard
EXAMPLES 1.about.9
Inorganic fine powders [precipitated barium sulfate (Examples
1.about.4 and 8.about.9), precipitated calcium carbonate (Examples
5 and 6) or magnesium oxide (Example 7)] having a specific surface
area and an average particle size indicated in Table 1 were added
to a linear low density polyethylene of MI=2 (L-LDPE (Examples
1.about.7)), a low density polyethylene of MI=5 (LDPE (Example 8))
or a polypropylene of MI=1.5 (PP (Example 9)) in quantities
indicated in Table 1, followed by blending the mixture by means of
Henschel mixer (tradename), pelletizing the blend, making the
pellets into a film by extrusion, and then uniaxially
roll-stretching the film to 2 to 7 times the original length at
50.degree. C. to obtain a porous film of 20 .mu.m thick. The
physical properties of the film were then measured. The results are
shown in Table 1.
EXAMPLE 10
A film made from the same composition as in Example 2 was stretched
(3.times.3) times in the longitudinal direction simultaneously with
the traverse direction at 70.degree. C. by means of a biaxially
stretching machine to obtain a porous film of 20 .mu.m thick. The
evaluation results of its physical properties are shown in Table
1.
EXAMPLE 11
Twenty % by weight of a linear low polyethylene (L-LDPE) of MI=2,
20% by weight of a low density polyethylene (LDPE) of MI=5 and 60%
by weight of precipitated barium sulfate having a specific surface
area of 4.1 m.sup.2 /g and an average particle size of 0.8 .mu.m
were blended to obtain a porous film in the same manner as in
Example 1. The evaluation results of its physical properties are
shown in Table 1.
COMPARATIVE EXAMPLES 1.about.6
Porous films were prepared in the same manner as in Example 1
except that an inorganic fine powders [precipitated barium sulfate
(Comparative Examples 1.about.3 and 5.about.6) or calcium carbonate
(Comparative Example 4)] under varied kinds, filled quantities and
stretching conditions as indicated in Table 1 was blended with a
L-LDPE in varied quantities. The evaluation results of their
physical properties are shown in Table 1. In Comparative Example 1,
since the quantity of fine powders added is less than 30%, the
porosity lowers and the water vapor permeability is small. In
Comparative Example 2, since the quantity of fine powders added
exceeds 80%, the stretchability lowers and stretching breakage
occurs in a stretching ratio of 1.5 times. In Comparative Examples
3 and 4, since the specific surface area of the fine powder exceeds
15 m.sup.2 /g, the stretchability lowered and foaming was observed
at the time of extrusion by means of a sheet molding machine, and
split. In Comparative Example 5, since the average particle size of
fine powders exceeds 4 .mu.m, the stretchability lowered so that it
is impossible to effect a stabilized production in a stretching
ratio of 2.0. In Comparative Example 6, since the stretching ratio
is less than twice, no sufficient water vapor permeability can be
obtained.
Since the film of the present invention is sufficiently porous, the
water vapor permeability and air permeability are good and also the
water resistance is superior. Particularly since its flexibility is
good to afford a soft hand, it is suitable for clothings,
particularly for sanitary use application. As compared with prior
art, it is possible to produce even an extremely thin film of 20
.mu.m thickness or less; thus the resulting porous film scarcely
has use application where it is used as a single product, but its
main use application is directed to its lamination onto non-woven
fabric, pulp, nylon taffeta, etc. The thinner the film, the less
the cost, and further, a specific feature is exhibited that at the
time of clothing, the fitting feeling due to the thickness of the
laminate is not uncomfortable.
TABLE 1
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Inorganic fine powders Basic resin Specific Average Tensile
strength Water Amount surface particle Amount Stretch at break
vapor added area size added ratio (kg) permeability Kind (wt %)
Kind (m.sup.2 /g) (.mu.m) (wt %) (times) MD TD (g/m.sup.2 24
Flexibility
__________________________________________________________________________
Example 1 L-LDPE 30 Precipitated 4.1 0.8 70 2 3.0 1.0 2000 A
BaSO.sub.4 2 " 40 Precipitated " " 60 5 4.0 0.5 3500 A BaSO.sub.4 3
" 65 Precipitated " " 35 7 5.5 0.3 2500 A BaSO.sub.4 4 " 50
Precipitated 8.0 0.5 50 6 5.0 0.4 3200 A BaSO.sub.4 5 " 40
Precipitated 14.0 0.5 60 4 5.8 0.4 2200 B CaCO.sub.3 6 " 60
Precipitated 5.5 3.0 40 5 4.2 0.5 2300 B CaCO.sub.3 7 " 50 MgO 7
1.1 50 5 4.3 0.4 2700 B 8 LDPE 40 Precipitated 4.1 0.8 60 4 3.0 0.3
1800 B BaSO.sub.4 9 PP 30 Precipitated 4.1 0.8 70 6 6.0 0.3 3200 B
BaSO.sub.4 10 L-LDPE 40 Precipitated 4.1 0.8 60 3 .times. 3 4.5 3.8
7000 A BaSO.sub.4 11 L-LDPE 40 Precipitated 4.1 0.8 60 6 4.5 0.3
3300 A LDPE BaSO.sub.4 Compara- tive ex. 1 L-LDPE 80 Precipitated
4.1 0.8 20 8 6.5 0.1 500 C BaSO.sub.4 2 " 10 Precipitated 4.1 0.8
90 BaSO.sub.4 3 " 50 Precipitated 18.3 0.3 50 BaSO.sub.4 4 " 70
CaCO.sub.3 16.5 1.0 30 5 " 60 Precipitated 0.8 4.5 40 2 2.8 0.8
1500 B BaSO.sub.4 6 " 40 Precipitated 4.1 0.8 60 1.5 2.5 1.5 100 C
BaSO.sub.4
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